1. Field of the Invention
The present invention relates to an image processing apparatus for processing input image data.
2. Related Background Art
Hitherto, for example, there have been known copying apparatuses as such a kind of image processing apparatus. Some such copying apparatuses have a magnification changing function to digitally read the original document image by a solid state image pickup device such as a line-shaped image scanner (CCD) or the like and to perform enlargment, reduction, or the like of the read image. As a general magnification changing method in those apparatuses, there has been known a method whereby the magnification in the feeding direction is changed by changing the scan velocity in the sub scan direction (direction of relative motion between original and scanner, to feed the image to the CCD). There has been known another method whereby the magnification in the main scan direction is changed by performing storage, thin-out, or the like of the pixels in the main scan direction (perpendicular to the feeding direction).
For example, when enlarging an image three times, assuming that the moving velocity in the sub-scan direction in the direct copy mode (i.e., at equal magnification) is V.sub.1, the moving direction of the sub-scan direction is set to V.sub.1 /3. With respect to the main scan direction, the image data of one pixel is repeatedly output three times. In this manner, a triple (output) size image is formed.
However, if the magnification changing process is performed by only the above method, as shown in FIG. 6, the enlarged output image has the same data on a three-pixel unit basis. Therefore, this method is preferably to enlarge characters, symbols, or the like having a single density. However, for example, in the case of changing the magnification of a half-tone image having a smooth density change such as in a photograph or the like, the foregoing method is unpreferable to obtain a smooth image.